An arrangement of the kind referred to above is known as a two-frequency laser interferometer and is disclosed in German patent application 3,616,393. The stabilization takes place by means of mechanical, thermal and electrical coupling of the two laser diodes to each other. Especially the long-term wavelength changes of laser diodes limit the quality that can be obtained therewith.
The stabilization of an individual laser diode by means of a Fabry-Perot interferometer is known and reliable.
The paper of R. A. Valenzuela et al entitled "Frequency Stabilization of AlGaAs Lasers to Absorption Spectrum of Rubidium using Zeeman Effect", Electronics Letters, Vol. 24, No. 12, June 9, 1988, pages 725 and 726, discloses the stabilization of a Fabry-Perot interferometer to an optical reference and the stabilization of a further light source to this Fabry-Perot interferometer. Here, a Fabry-Perot interferometer is driven with two light sources but only one type of light, namely, that of the laser diode is made available as a use light.